1. Field of the invention
The invention pertains to a method of reclaiming a plastic product, such as a bumper of an automobile, having a paint film coated on the surface thereof. More particularly, the invention is directed to a method of reclaiming a plastic product by producing a plastic body while separating a cured paint film from the surface of the plastic body.
2. Prior art
Plastic products generally have excellent corrosion resistance. Because of good corrosion resistance the plastic products are difficult to bring back to nature when scrapped and therefore liable to cause environmental problems if left untreated. Since resources are finite, they must be utilized effectively. Hence, it is desired that plastic waste be collected and reclaimed.
If a plastic product is made of a single material, the plastic product is comparatively easy to re-use because such product can be collected and fused to be pelletized. However, if a plastic product is made up of a plastic body and other kinds of resins, the re-use of the product is generally limited because collection and separation of the other kinds of resins from the plastic body is difficult. Cabinets of electrical appliances, e.g., are formed of a plastic and are coated in a variety of colors from design considerations. It is difficult to collect only a plastic body from a plastic product having such a paint film.
To overcome this problem, plastic products having a paint film are often crushed without separating the cured paint film therefrom and formed into reclaimed products by an extruder, press-forming equipment or the like.
A reclaiming method involving separation and removal of the paint film has recently been studied, and a method of separating a paint film by means of an organic solvent is proposed. The proposed method includes the steps of: crushing a plastic product having a paint film; separating the paint film by dipping the crushed pieces into a solvent consisting essentially of an organic salt or the like; separating the plastic body from the crushed pieces; rinsing the plastic body with water and drying the rinsed plastic body; and pelletizing the thus processed plastic body with an extruder or the like. Another method is also proposed. This method is characterized as causing the crushed pieces to come in contact with a solvent consisting essentially of an organic salt or the like under high temperature and pressure to chemically decompose the paint film.
The method of forming a reclaimed product with an extruder or the like by directly crushing a plastic product having a paint film without separating the paint film from the plastic body is economically advantageous in that what is required is only crush the collected plastic product.
However, the paint film or the paint is mixed in the crushed pieces, and this makes the formed reclaimed product inferior in quality and limited in application.
To overcome this problem, the paint film is separated and removed from the fused plastic by inserting a plurality of screens of high meshes in combination into an end of the extruder. Such separating and removing method is advantageous in terms of efficiency. However, the availability of screens of desired meshes is limited. As a result, film pieces finer than the available meshes still remain, thus making the appearance of the formed product poor. In addition, the mixture of foreign matter such as the paint film pieces makes the formed reclaimed product insufficient in strength, which has been verified by the inventors. Therefore, applications for the reclaimed plastic recovered by means of the above-described methods are limited to, e.g., making benches in parks, fence, and blocks for pavements.
To overcome the low quality and limited use, attempts have been made not only to pulverize the paint film to sizes smaller than 10 .mu.m, but also to reduce the ratio of mixing the paint film in the reclaimed plastic. The results are, however, not satisfactory. Even with a plastic product such as a bumper of an automobile whose film mixing ratio is about 2% by weight which is relatively low, an addition of 80 to 90% of new plastic per bumper is required to reduce the film mixing ratio; otherwise, the formed reclaimed product does not meet quality requirements, nor is such product practically applicable. Even if a kneading disc or a reversible screw is used to improve kneading and screens are used for filtration in order to make the paint film pieces still finer and low mixing ratio, it is extremely difficult to pulverize the paint film pieces to sizes smaller than 10 .mu.m. As a result, some practical problems are imposed to be solved.
The method of separating the paint film with an organic solvent allows the plastic body to be separated, but is cumbersome because the paint film must be scraped off after swollen by a solvent such as an organic salt. In addition, this method demands not only a large cost in treating the waste solvent in order to prevent environmental pollution, but also a large amount of water for rinsing plastic, and is likely to involve large equipment. The paint film is separated from the plastic body in the solvent easily. However, since the specific gravities of the paint film and the plastic body are larger than that of the solvent, the paint film and the plastic body get settled down together. As a result, it is extremely difficult to separate only the plastic body from the solvent containing both the paint film and the plastic body to an appropriate degree of accuracy. Thus, mixture of the paint film pieces in the plastic body is unavoidable, making the reclaimed product poor in quality even if the reclaimed method uses the organic solvent.
The method of chemically decomposing the paint film by increasing the temperature and pressure of an autoclave allows the plastic body alone to be separated with efficient decomposition of the paint film. However, the method also involves large equipment, demands a large cost in treating the waste solution, and is time-consuming to completely decompose the paint film. In addition, the batch operation makes the process less productive. The separated plastic body must be washed to remove the adhering solvent and pelletized by an extruder thereafter, thus making the process complicated and inefficient.